20 research outputs found
Quantum spin liquid signatures in Kitaev-like frustrated magnets
Motivated by recent experiments on -RuCl, we investigate a
possible quantum spin liquid ground state of the honeycomb-lattice spin model
with bond-dependent interactions. We consider the model, where
and represent the Kitaev and symmetric-anisotropic interactions
between spin-1/2 moments on the honeycomb lattice. Using the infinite density
matrix renormalization group (iDMRG), we provide compelling evidence for the
existence of quantum spin liquid phases in an extended region of the phase
diagram. In particular, we use transfer matrix spectra to show the evolution of
two-particle excitations with well-defined two-dimensional dispersion, which is
a strong signature of quantum spin liquid. These results are compared with
predictions from Majorana mean-field theory and used to infer the quasiparticle
excitation spectra. Further, we compute the dynamical structure factor using
finite size cluster computations and show that the results resemble the
scattering continuum seen in neutron scattering experiments on
-RuCl. We discuss these results in light of recent and future
experiments.Comment: Modified manuscript: 17 pages, 21 figure
Sedentism and plant cultivation in northeast China emerged during affluent conditions
The reasons and processes that led hunter-gatherers to transition into a sedentary and agricultural way of life are a fundamental unresolved question of human history. Here we present results of excavations of two single-occupation early Neolithic sites (dated to 7.9 and 7.4 ka) and two high-resolution archaeological surveys in northeast China, which capture the earliest stages of sedentism and millet cultivation in the second oldest center of domestication in the Old World. The transition to sedentism coincided with a significant transition to wetter conditions in north China, at 8.1–7.9 ka. We suggest that these wetter conditions were an empirical precondition that facilitated the complex transitional process to sedentism and eventually millet domestication in north China. Interestingly, sedentism and plant domestication followed different trajectories. The sedentary way of life and cultural norms evolved rapidly, within a few hundred years, we find complex sedentary villages inhabiting the landscape. However, the process of plant domestication, progressed slowly over several millennia. Our earliest evidence for the beginning of the domestication process appear in the context of an already complex sedentary village (late Xinglongwa culture), a half millennia after the onset of cultivation, and even in this phase domesticated plants and animals were rare, suggesting that the transition to domesticated (sensu stricto) plants in affluent areas might have not played a substantial role in the transition to sedentary societies
Inhomogeneous Phases in a Double-Exchange Magnet with Long Range Coulomb Interactions
We consider a model with competing double-exchange (ferromagnetic) and
super-exchange (anti-ferromagnetic) interactions in the regime where phase
separation takes place. The presence of a long range Coulomb interaction
frustrates a macroscopic phase separation, and favors microscopically
inhomogeneous configurations. We use the variational Hartree-Fock approach, in
conjunction with Monte-Carlo simulations to study the geometry of such
configurations in a two-dimensional system. We find that an array of diamond
shaped ferromagnetic droplets is the preferred configuration at low electronic
densities, while alternating ferromagnetic and anti-ferromagnetic diagonal
stripes emerge at higher densities. These findings are expected to be relevant
for thin films of colossal magneto-resistive manganates.Comment: 15 pages, 9 figures. Journal Ref. added, errors correcte